1. Field of the Invention
The present invention relates generally to the construction of pneumatic tires, and more particularly, but not by way of limitation, to improved constructions for the turn-up endings of the body plies in the sidewall region of a tire.
2. Description of the Prior Art
A typical prior art tire construction for a tire having two body plies in each sidewall is illustrated in FIGS. 1A-1E. In FIG. 1A, first and second body ply sheets 10 and 12 are being placed on a tire building drum 14. The first sheet 10 is shown as being wider than the second sheet 12. In FIG. 1B the first and second sheets 10 and 12 are in place around the tire building drum 14. In FIG. 1C tire bead rings 16 have been placed around the tire building drum. In FIG. 1D the axially outer portions of the body ply sheets have been folded over the bead rings as indicated by arrows 18.
FIG. 1E is a schematic cross-section view of a typical prior art tire construction utilizing the tire carcass constructed in accordance with FIGS. 1A-1D. In each sidewall of the tire the body ply sheets 10 and 12 terminate in free turn-up ends 20 and 22, respectively.
Tire constructions such as that shown in FIGS. 1A-1E are commonly designed with radial or bias body plies that have such free turn-up ends, which may also be referred to as discontinuous body ply endings, in the sidewall region. The free turn-up ends can provide an origination point for cracking in the adjacent rubber matrix, especially during severe operating conditions such as under inflation and/or overloading of the tire. This under inflation or overloading can lead to extreme flexion of the tire in the sidewall area, and that flexion can ultimately lead to fatigue type conditions originating adjacent the free turn-up ends.
This is particularly a concern in agricultural tires which are designed for operation at relatively low pressures in order to increase the footprint of the tires to reduce soil compaction. Such agricultural tires designed for low pressure operation and heavy loads are at increased risk for sidewall conditions of the type described.
Accordingly, there is a continuing need for the enhancement of tire designs to provide robust constructions that can withstand the expected conditions of high flexion due to low pressure and high load operation.